Field of the Invention
The present invention relates to a combined cycle power plant and a start-up method of the combined cycle power plant.
Background Art
In a combined cycle power plant, exhaust gas discharged after being used in a gas turbine is guided to an exhaust heat recovery boiler, then steam is generated using exhaust heat which is recovered, and then a steam turbine is driven using the steam. Since an amount of power generation significantly varies in a power plant using renewable energy represented by wind power or solar power, it is demanded to shorten the start-up time of the combined cycle power plant such that instability of a power system is reduced.
Therefore, at the time of start-up of the combined cycle power plant, the steam, which is supplied to the steam turbine, needs to have a rapid increase in temperature and a flow rate. However, as a result, a front surface of a turbine rotor has a more rapid increase in temperature than the inside thereof, which results in a temperature gradient in a radial direction of the turbine rotor, and thus thermal stress is increased. A large increase in the thermal stress can cause a reduction in the service life of the turbine rotor. In addition, in a case where the steam has a significant temperature change, a difference in thermal expansion is generated between the turbine rotor and a casing due to a difference in heat capacity. When the difference in thermal expansion is increased, there is a possibility that the rotating turbine rotor and the stationary casing come into contact with each other and are damaged. Therefore, there is a need to appropriately control the temperature or the flow rate of the steam at the time of start-up such that the thermal stress or the difference in thermal expansion does not exceed a limit value.
Here, regarding start-up control of a steam turbine, technology is known, in which a high-speed start-up of a steam turbine is performed, in a condition in which thermal stress and a difference in thermal expansion in a certain period of time from a current time point are predicted and calculated, and predicted values of the thermal stress and the difference in thermal expansion are each controlled to be smaller than a limit value (see JP-2009-281248-A). In JP-2009-281248-A, the thermal stress and the difference in thermal expansion are predicted and calculated based on a measurement value of a state quantity (specifically, for example, a temperature or pressure of steam in an inlet of the steam turbine) of a plant, and then an amount for a plant operation is determined such that the predicted values are each smaller than the limit value.